The present invention relates to restraint systems and in particular to a latching restraint system which latches during a crash, and remains latched until a release is actuated.
Generally, automotive and FM shoulder strap type Inertial Reels (IRs) are of the lock/unlock type. That is, the IR will lock to protect the occupant at the onset of either vehicle motion or shoulder strap acceleration above a first higher preset acceleration level, and automatically unlock when the acceleration level drops below a second lower preset acceleration level. The acceleration levels are usually set at very low thresholds. The low thresholds insure consistent IR locking in crash situations. After the acceleration level event passes, the IR automatically unlocks to allow normal operation of the restraint system with flexibility for the occupant to move within the constraints of the maximum extension bounds of the restraint system.
Unfortunately, a problem may occur with lock/unlock type restraint systems in certain crash or other scenarios. The onset of multiple discreet lock (or crash) events and the ability to unlock between events could allow the occupant to move away from a protected position where his shoulders are held tightly to the seat back. A typical event is an extended crash scenario where second and third impacts occur following the initial impact, for example, a military vehicle involved in a bomb blast from underneath. The initial concussion causes the restraint to lock. The trajectory of the vehicle will allow the restraint system to unlock as the vehicle ascends and then returns to earth. While the restraint system is unlocked, the occupant may become displaced from the protected position. When the vehicle impacts the ground, the occupant is free to impact the vehicle interior. The risk of injury is significantly higher in such situations. Similar scenarios may be predicted for multiple independent crash events with civilian vehicles, particularly after an airbag deflates.
Additionally, vehicle seats often have occupant restraint systems mounted to the seat. As a result, the seats must bear crash loads through the structure of the seat. The resulting forces on the seat structures, and the forces at the seat to vehicle mounting points, are often significant, and substantial displacement of the vehicle occupants may result.